The invention relates to a telescopic steering column, in particular for a motor vehicle, having an outer column tube and a stem, the column tube and the stem being connected by means of a deformation body.
Such steering columns are frequently used in modern motor vehicles and are thus known. In this case, the deformation body prevents the deformation forces which act on the vehicle in the event of an accident from reacting on the driver. In particular, an axial displacement of the steering column into the passenger space is prevented. In some embodiments, the deformation body is also used to keep the risk of injury as small as possible in the event of the driver hitting the steering wheel.
To this end, the deformation body is provided, for example, with a predetermined breaking or tearing point, which enables the stem to be pushed telescopically into the outer column tube as soon as a predetermined maximum force is exceeded. In this case, the stem and the outer column tube are firmly connected to one another in normal driving operation. To this end, the deformation body, according to a known configuration, is made as a tear strap, the stem being torn open to the outside in the event of an excessive action of force.
A disadvantage with deformation bodies designed in such a way is that adaptation to the desired deformation forces involves considerable outlay and to this end, reconstruction of the steering column is usually necessary. Furthermore, inadvertent tearing of the deformation body in normal driving operation must be reliably avoided and at the same time reliable separation of stem and column tube above the admissible value must be ensured. At the same time, even slight production tolerances have an adverse effect on the operating reliability of the steering pillar. Therefore, many steering columns used in practice have a deformation body in which deformation is not effected until the action of a relatively large external force and the driver is thus subjected to high loading.
The problem underlying the invention is to provide, a steering column of the type mentioned at the beginning in such a way that this steering column permits reliable transmission of the steering forces in normal driving operation and at the same time prevents transmission of external forces to the driver above a value which can be freely set. In this case, production tolerances are at the same time to have no effects or only insignificant effects on the operating reliabilty, and the assembly process as well as the adaptation to various intended uses are to be facilitated.
This problem is solved according to the invention in that the deformation body has a shearing body, which has a shearing area differing from its cross-sectional area. In this way, it is possible to reliably connect the column tube and the stem by means of the shearing body and at the same time establish a desired, maximum transmittable force by adaptation of the shearing area. In this case, the shearing body may in particular have dimensions which permit a simple and perfect connection in the assembly process. As a result, for example, production processes which have comparatively high tolerance values or require specific shaping of the shearing body may also be used. The adaptation of the desired shearing forces permits universal use of the shearing body in different vehicles.
An especially advantageous development of the invention is provided by virtue of the fact that the shearing body, in its installed position, in the region between the column tube and the stem, has a shearing area reduced relative to the remaining cross-sectional area. As a result, the shearing body can have a cross-sectional area designed in accordance with the steering forces to be transmitted and to this end may also be provided, for example, with a thread or a special profile, the shearing body having a reduced shearing area which is independent thereof.
An especially favorable development of the invention is also provided when the shearing body has two sections, which are connected to one another in a positive-locking manner by means of a shearing pin determining the shearing area. By the division of the shearing body into two sections, the forces acting in the parting plane are transmitted solely by the shearing pin. In this case, the two sections bear directly against one another and thus permit transmission of virtually unchanged thrust forces in the plane transversely to the parting plane. As a result, the shearing body designed in such a way may also be driven into the steering pillar with a relatively large force. In this case, the first section is connected to the outer shaped body and the second section is connected to the stem.
In this case, the shearing pin may have any desired dimensions and different material properties and may be connected to the two sections in a detachable or fixed manner. An especially expedient connection is also provided by virtue of the fact that the shearing pin has a press fit. In this way, the two sections of the shearing body may first of all be joined together to form a construction unit, so that the subsequent production process is substantially facilitated. In the process, the shearing force can at the same time also be determined in a precise and reliable manner and incorrect assembly can be prevented.
An especially simple embodiment of the invention is also provided by virtue of the fact that the shearing body has a first section, which is provided with a projection and is inserted into a corresponding recess of a second section. In this way, the assembly process can be further simplified by virtue of the fact that the shearing body consists of only two parts. In this case, different configurations for facilitating the assembly may be provided, in which case, for example, the external dimensions are standardized even in the case of different shearing areas.
The invention is configured in an especially simple manner in that the shearing body has a core, which can be removed after the insertion of the shearing body into the steering column.
To this end, during the assembly process, the shearing body may be designed in particular as a solid shaped part, which in this way permits problem-free production and the transmission of high assembly forces. After the subsequent removal of the core, which to this end, for example, is specifically inserted beforehand into the shearing body, the cross-sectional area is reduced to the desired shearing area. Embodiments in which the core of the shearing body is removed by any desired processing, for example by machining, are just as conceivable as the use of a core provided with differing material properties. The core may also be designed as part of a tool and as a result may be inserted into the hearing body merely during the assembly process.
An especially effective modification of the invention is provide by virtue of the fact that the shearing body has a least one aperture reducing the cross-sectional area to the size of the shearing area. Such an aperture is easy to make and thus permits a rapid adaptation to he admissible shearing forces.
It is also especially advantageous if the shearing body has an essentially circular cross-sectional area. In this way, assembly errors can be largely eliminated. At the same time, notch effects due to edges on the shearing body and the associated effects on the admissible sharing stress can be prevented.
An especially suitable embodiment of the invention is also provided by virtue of the fact that the steering column has a plurality of shearing bodies distributed approximately uniformly over the circumference. Possible influences due to bending moments on the shearing body can thereby be largely avoided. In this case, a plurality of the shearing bodies may also be combined to form a construction unit, or a shearing body may have a plurality of shearing areas distributed over the circumference.
It is favorable in this connection if the shearing body is made of steel. As a result, the material properties the shearing body designed in such a way can also be adapted to high loads. At the same time, the sharing body is insensitive to temperature fluctuations and corrosion.
The outer column tube and the stem may be inserted into one another in a positive-locking manner, so that a rotary movement relative to one another is limited so as to be small or is completely ruled out. However, it is especially advantageous if the outer column tube and the stem are connected in a rotationally locked manner merely by means of the shearing body. As a result, in the event of an excessive action of force on the steering column, transmission of axial and radial forces is prevented. The passive safety of the driver is thereby substantially increased.